Black Screen / Can't See Videos

I have been trying to play a video on my PC and the audio works fine but I can only see a black screen. I downloaded codec but still no picture. This has happened before but it's been a long long time. Any suggestions? (Slingbox and internet videos are fine -- only DVDs or copies of DVDs cause the black screen).

What player do you use?
Will VLC work?
http://www.videolan.org/vlc/